Line circuit communication system



Jan. 18, 1949. F. w. BRIXNER ETAL LINE CIRCUIT COMMUNICATION SYSTEMFiled Jan. 26, 1948 m 4 BE; m2: 385%: EU zocumn fi IE? ELQEE 55% E55 38TJ J T {111... new m Pr! v vm m: m illl ill. SN

r SIK V Rr E O N Ta R m y m W M I W M r PIY NEENGU L 3 e V Q m 3m q 5 uf MEIQEOEZS 2Q PS ZOE. Eh QPZQ mum I836 QEQEE U75 SEQ SE28 Patented Jan.18, 1949 UNIT ED? OFFICE LINE"CIRGUIT GOMMUNICATION SYSTEM Frederick..Brixnen. Gates, and. William. M.. Barker, Greece, Nl'Yigassignors.t'o'General Railway .Signal, Company; Rochester; Ni YiApplicatibmJanuam-ZG, 19.48, SeriaLNo. 4,418.

6 Claims. (01. 177453) 11 l This. invention relates; to. line-circuitcommunication. systems, and; it more. particularly pertains. to. meansfor transferring. a; linercircuit. used'for direct. and foralternating... current communication from one pair oifllinerwirestolthe.other.

In a line: circuit communication system. such asa centralized trafiic.control system for railroads,..conveniently termed aCIJZC system, a.central control oflice. governstiafiicv throughx aapan ticular. assignedterritory by line circuit communication. ofcontroll and indication. It.is often,

desirable to locate the control oflice in a. downtown office building,on the.like, remote.from the CTC territory with which the. controloffice is.

associated, inorder to takeadvantage of central ofllcefacilities. Undersuch. conditionsthe connection. of .the. oiiiceto communication linewires at the. beginningof. the C'I'C'iterritory is often accompli'shedthrough aerial and/r under ground cable, or the like, which isnecessarily somewhat" subject to damage as the result of weatherconditions orasxaresult oi damaeeworkmen. the maintenance. ofcommunication. wires which may.v

be. closely. associated therewith. It is therefore desirable to. providespare line Wires, preferably indifferent cables anddifiierently routed,to which the CTC line .circuit' can. be transferred in. case of loss ofcontinuity through one .pair ofline wires, ,or in case. of otherlineicircuit" difiiculties; interfering with the communication of?controls. and indications between. theicontrolofiiceand" the OTCterritory with which it is'associ'ated:'

An objectofth'e present inventionis toprovide means responsive to'manual designation" by; an operator" atthe control oificeicr-transier-of a CTC line circuit from one pair ofilin'ewiresto anotherina manner was to isolate onepair of line wires at both ends fromtheotherpair:

Another object of" the present invention-istw render theshifting fromone linecircuit=to-the-- other-effective through a carrier repeaterstation soa s to -effect the transferof thecircuit extend the idle lineewires in. combination with .a. locally" energized transfer stickirelay.

Another. objectof thepresent inventiontistoz useatheline circuittransfer means atthe, repeater. station to: shift .to: "standbyrepeater; apparatusiin response. to manual; desie'nation at the. controloffice.

Other objects purposes and. characteristic tea.- tures. of thepresentliinventi'on willlbedn. part obj-- vious from theaccompanying-drawings, andin part poi'ntedlout as: the description. ofthe invention. progresses.

is made to the accompanying.drawlngswhich illustrates schematically,with some parts. shown. in

block form,. an organizationior the transfer of. a C'ICdin'ecircuit fromone pairtofli'ne wires to used inthe" drawing as representati'ngconnections torespectivepositiveand negative-terminals: of. suitablebatteries" or other sources of "direct" current.

Inasmuch" as theispecific character ofthe CTC' transmitting" andreceiving apparatus for" communication of controlsand-indications-overthe line circuit has little "bearing on the presentinvention, for thepurpose of simplification of=this embodiment of the-present invention;such appaartus has been-indicated on the" drawings in block form; andit' is'to be-understood that this appaart'us Whichis well known tc==those familiar with the-artis provided according" to the re quirement-sof practicer If desimedythe D. CJ-CTC" transmitting-and receivingapparatus can be-dis-'- closed; for"examplein the patent mew; D5 Haileset-al. No. 2*,3'99'5734, dated 'May '7 ;'194'6? For this embodiment ofthe present invention,v it is assumed thatiboth direct current GTCpulsesand alternating current carrier pulses are-trans mitted: overthe-dine wires illustrated in the: drawings; The directcurrentpulses'arausediior the communication? on controls-andindicationstor a firstsection of the: territory for:which the CTIIG',icontriolcmachinesris providedu and the: car rieri apparatus: is- -u'sedifiorithe communicationzofza controls and indications overthe.linetwiresrandt through :the. first sections otxithe CfIKCL.territory 1 to a suitable. connerteri: station. where: carrier: puises:fiGIEJthG'." communination of? controls are converted .iniinir direct.cunrenin pulses; anntthe.

direct currentzindieation pulsessreceivedxrhy.such.

comzerter 'statiomf-nomcthe: secondrsection; of? the. C'IiC,.territonyr;an t. converted iintotcarrien r pulses fort communinati'om through the:first sectiomofi; therCTC territory and; the: line; .wireszillustratedcin the: drawinga- .toiu theecontrol 5 01116815 It-Jiss Dfzi courseramattenrofi choiceizasto wthew frequencies; used-.iomcarriercommunication oft controls; and indications; and itthaswbeenfGHHdrzfihflfilCfliIIiBI frequency; currents-in; the band from. 10to-.2G Inca.

are satisfactory, distinctive frequencies bein generally employed forthe communication of controls and indications.

Because of attenuation of the carrier pulses, carrier repeater stationsare required at intervals for amplification of the carrier pulses, andthus the carrier repeater units Nos. 1 and 2 are provided at the carrierstation illustrated in the accompanying drawing for repeating thecarrier pulses received from the control ofi'lce into the line wires L1and L2 extending in the direction of the CTC territory.

Each of the carrier repeaters illustrated in block form in theaccompanying drawings is to be understood as including electronicamplification means for amplifying the respective control and indicationfrequency currents, the'wires Ill and l I being the in-put wires for thecommunication of controls and the out-put wires for the communication ofindications for the carrier repeater No. 1. The wires l2 and [3 are theout-put wires of the carrier repeater No. 1 for the communication ofcontrols and the in-put wires for the communication of indications. Thecarrier repeater No. 1 is illustrated as being associated with the linewire ILI and IL2 as selected by the position of the carrier repeatertransfer switch CTS, such switch being effective in a manner to behereinafter considered to select between carrier repeater No. 1 andcarrier repeater No. 2. It is thus provided that only one of the carrierrepeaters is used at a time, two identical carrier repeaters beingprovided so as to cause a minimum interruption of service in case offailure of the electronic control apparatus associated with anyonecarrier repeater unit. the carrier repeater No. 2 can be consideredas a standby carrier repeater although means is provided as herinafterconsidered for manually selecting as to which repeater is to be thestandby repeater The wires ILI and IL2? constitute one pair of linewires, which may or may not be in aerial or underground cable, forconnection of the portion of the CTC line circuit. connecting thecontrol office and the repeater station, and the wires 2L1 and 2L2constitute a second pair of line wires, conveniently called standbywires extending between the control oflice and the repeater station towhich the line circuit can be shifted as required. It is of coursedesirable that the respective pairs of wires be routed separately asmuch as possible so as to reduce the possibility of failure of bothpairs of wires at the same time. In a similar manner the wires ILI? andIL2 constitute one pair of line wires connecting the repeater locationand the beginning 'of CTC territory, and the wires 2Ll and LL2constitute the second or standby pair of wires extendingbetween thesepoints.

At the control oifi'ce the line transfer switch LTS is locatedconvenient to the operator of the control machine, preferably on thepanel of the control machine, and it is provided as a means for manualdesignation of the particular pairs of wires and the particular carrierrepeaters that are to be used in the line circuit of the CTC com-'munication system. Associated with the line transfer switch at thecontrol office is a line transfer relay LT, the contacts of whichdirectly select as to which of the pairs of line wires extending fromthe control office is to be connected to the CTC carrier transmitter andreceiver at the control office. It is to be understood that the relay LTis used in combination with the In other words particular pair of linewires that has been idle in a manner to be more clearly understood whenconsidering the mode of operation of the organization. In a similarmanner, at the beginning of the CTC territory, the relays LIl and LTZare provided for transfer purposes, such relays being associated withthe respective pairs of line wires extending between the repeaterstation and the beginning of the CTC territory.

Stick relays LTP and LT]? are provided respectively at the repeaterstation and at the beginning of the CTC territory for transfer purposes, such relays being controlled by the associated relays LTI and LT2at such locations. A relay CTR at the repeater station is used totransfer from one repeater unit to the other at the repeater station inresponse to the actuation of switch LTS at the control oflice. It alsois used to select the application of power to the particular carrierrep-eater unit that is to be rend'ered active.

Having thus considered the general organization of the system accordingto the embodiment of the present invention illustrated in theaccompanying drawing, the organization will hereinafter be morespecifically considered upon considering typical conditions of operationto be encountered in practice.

Operation It has been illustrated in the drawings that the line wires ILi and IL2 are connected so as to be in use in the CTC line circuitunder conditions that may, for the purpose of facilitating thedescription of the present invention, be assumed to be the normalconditions of the system. Similarly the carrier repeater No. 1 and theline wires ILI and IL2 are in use during the normal conditions of thesystem.

In accordance with the general principles of operation of the abovementioned CTC system as disclosed in the patent to W. D. Hailes et al.No. 2,399,734, the line circuit is normally energized during a period ofrest when no controls or indications are being communicated and suchenergization can-be traced to connect the positive terminal of the linebattery CB to the line wire L2 =at the beginning of the first section ofCTC territory, through selections of the CTC apparatus at the controloffices, wire L2, back contact [5 of relay LT, wire ILZ back contact 18'the beginning of the first section of CTC territory through selectionsof the D. C.-CTC transmitter and'receiver at the control office, wireLl, back contact [4 of relay LT, wire ILI back contact 22 of relay LTP,choke l6, back contact 23 of relay LTP, wire ILI back contact 24 ofrelay LTP and winding 25 of the impedance matching transformer 28.

it will'lbe noted mm the selecticnthat hasjust been traced for theeonm'ection ofthe control bat-- tery CB to the line wires L1 andLlth'at'there are no line transfer relays ii'I-l' or LTTenergizedbythe-iine circuit at* thistiine as such relays areenergi'zed onlymomentarily-upon shifting to the alternate pair of'lihe wires aswill behereinafter" considered; In-addition'to the-"direct cur 1 rent CTCcircuit connections as hasqbeenjust- CTC transmitter and" andLZL;

The. transmission-Maire carrier currents; however isblocked-in therepeater station by'the receiver to thewires' Ll choke; coils Hiandllandthus rather than being directly" connected through" the repeaterstation, the control carrier-frequency currents are fed as. in -put tothecarrier repeater No. 1 in which they are amplifiedandappliedasout-put to theline wires; extendingto the CTC territory. Indicationcarrier current pulsesarefed' back from the C'IC territory to. thecontrol oiiice at a distinctive frequency over the same circuit.

Itis. therefore proyided;thatthe. carrier.current pulses for thecommunicationof controls are transmitted from thecontrol'oflice andapplied across the wires IU'andQ-ITI' lof vth'ecarri'er repeater No. 1.Ifhe wire Lll-of'the. OTC" transmitter at the. control oificeisconnectedtc the wire, HJJof carrier repeater No. 1 through back contactI 5 of relay. LT, wire. I.L2 backxccntacti l8. of relay.

L'I'Pand back contact 26.. off relay CTR. The wire Lllof the OTCtransmitters. atthe control office is. connected to thewine Hofflthecarrier repeater No. 1. at the repeater station through backcontact M ni. relay LT, wire. l.L.I.1 ,.backccntact. 2.2 of relay LTPand back. contact 2'! of relay CTR! o The carrier repeater. No.L-isconnected'to the impedance matching. transformer. 28 by a. circuitincludingwire |2..of carrier repeatenNd. 1, back,

contactlza of relay CTR, backcontact [9 .of relay LTP; wire iLZZ; backcontact 20 0f; relay LTP winding 30 of. the impedace. matching. trans-vformer 28,. coupling. condensenCl, winding 3| of the impedance matchingtransformer 28., .back.

contact 24' 'ofrelay LTP wire ILW, back. contact 23 of relay L'IP; andback contact; 32.. of, relay CTR to the wire [3' of the carrierrepeaterNo. 1.

The line wires LI? and. L2 are connected 23; being assumedfto be. in acable having re1a-. It is to. be understood.

tively lower impedance. that if no impedance matching is required underthese conditions, the impedance matching transformer Z8. is not requiredand the wires LI and L2 are energized directly fromfthe contacts of therelay LTP The condenser C l is included in the transformer circuit as ablocking. condenser for direct current energization ofthe line wires. Itwill be seen from the. organization as it has been described'up to thispointthat there are rawings is connected in multiplewith' the D. -01-several poss'ibilitiea ottfailune .inrthe integrity? 0:14

the line circuit betweenthe controtoflice and the CTC" territorywhicirican cause failure: of- :the. OTC system to operaterproperlm. Qne.of;thesew conclitionsis in the line wiresJLH andiLZ either of whichmaybecome. open circuited; or. these:

wires may become short. circuited'because of.

damage to the cable.- Similarlythe wires: ILA? and;

IL2 extending f'rom the: repeaters station to the first section ofCTU'territory may become. open: circuited' or short circuitedtorcausefailure of. proper operation of the OTC system. Because ofthecarrierrepeater-Not 1' atthe repeatersstation being' 'dependent. uponelectronictubea a failure of the electronic apparatus: can interrupt:theservice between the contr olofi'ce and the: OTC territory, thusmaking it desirable to beable to transfer tothe stand-bycarrirrepeater-ap. paratus No. 2.

If failure occurs under any one of'inore of the three abovedescribedconditions, the operator at the control ofiice uponbecomingaware of the failure, may; by actuation of the line' transier switchL'IS-on the control panel of the control machine, cause the-transfer ofthen C. and

A. (3'. communication line circuitsfromthe-nor-- mal line Wires ILI andlL2 to the standby line wires 2Ll and 2L2 Iirresponse'to the-trail forbeing rendered effective at the-repeatersta tion, energy isapplied tothe standby wires 2-Ll and LL2 so as to complete the-transfer totheseWires at the location of thebeginning ofCTC territory. Also atransferiseflective to shift from the carrier repeater station-No; 1* tothe'sta-ndby carrier repeater No. 2.

the consider more specifically: the manner in; which the above describedtransfer operation is effective, the actuationof *theswitc'h LTS at'thecontrol office is effective to pick up. the relay LT and. open theconnection of the wires LI, and L2 tothe wires lLI and ILZ at'backcontacts It and Hi, respectively; The shifting of contacts I4 andI51 of relay LT; (upon the picking; up of that relay, connects the wires2Ll and 2L2 to the wires LI and. L2; respectively. Because of'direct:current energy being, applied bythe D. C'.-CTC transmitter at thecontrol office to thewires Hil and 2L2 through the front contacts l4 andI5 of relay LT, the relay LTZ at the repeater station becomes energizedby a circuit extending. from the wire Llat the control .ofli'ce,including front contact 54 of relay LT,wire 2Ll back contact 33 of relayLTP, winding of relay LTZ, back contact 34 of relay LTP, Wire 2L2andfront. contact l5 of relay LT, tothe wire L2.

Upon the pickingup. of relay LT2,Ithe stick relay LTP is pickedlup bytheclosure of front contact 35,. and. the picking up of that relay es-'tablishes a stick circuit extending from in cluding back contact 36' ofrelay LTl, front contactii'l of relay LTP. and winding of relay LTP, toBy this stick circuit, pickup contact 35 is shunted out, and it isprovided'that the restora-. tion. of relay LTP can be accomplished onlyby the subsequent picking up, of the relay L'Ii at a time when anoperatoratthe control office designates the restoration to the formerline circuit by the restoration of the switch LTS to its normally openposition. The picking up of the relay LTP, by the openingofback contacts33and 3 4- deenergizes the relay LTZ and thus provides that" the. relayLTZ is disconnected from the line circuit and. dropped. away immediatelysubsequent to the picking up of relay LTP.

The closure of front contact 34', ofrelay' LTP provides that directcurrent energy is applied from wire 2L? to the wire 2L2 through thechoke l1 and front contact [9 of relay LTP. Similarly the wire 2Ll isconnected to the wire 2L| through front contact 33 of relay LTP, chokel6, and front contact 23 of relay LTP. It is thus provided that directcurrent energy is fed from the control battery CB at the control officethrough the back contacts 38 and 39 of relay LTP to the winding of relayLT2 at the location of the beginning of the first section of CTCterritory. s n

The picking up of relay LT2 by the closure of front contact 48 causesthe picking up of the re lay LTP which is maintained picked up by itsstick circuit extending from including back contact 4! of relay LTIfront contact 42 of relay LTP and winding of relay LTP to The relay LTPwhen picked up connects the wire 2L! through front contact 38 to the impedance matching transformer 28, and the closure of front contact 3c ofrelay LTP connects the wire 2L2 to the impedance matching transformer28. It is thus provided by the mode of operation as above described thatthe D. C.-CTC line circuit is shifted to the standby circuits extendingfrom the control office to the repeater station and from the repeaterstation to the beginning of the first section of CTC territory.

The carrier current line circuit is necessarily similarly shifted inthat it involves the use of the same line wires, and in addition, thereis an automatic shift from the carrier repeater unit No. 1 to thecarrier repeater unit No. 2. This is accomplished by the picking up ofthe relay CTR y:

at the repeater station in response to the picking up of relay LTP.Relay CTR is picked up by 'a circuit extending from including the frontcontact 49 of relay LTP, contact of the carrier transfer switch CTS inits left hand position, and Winding of the relay CTR, to The picking .upof relay CTR, by the shifting of contacts 26 and 21 opens theconnections to the wires l and H of carrier repeater No. 1 and closesconnections to corresponding wires 43 and 44 of carrier repeater No. 2.Similarly the shifting of contact 32 opens the connection of the wire [3of the carrier repeater No, l and closes a connection for thecorresponding wire 45 of the carrier repeater No. 2. The shifting of thecontact 29 opens the connection of the wire I2 associated with thecarrier repeater No. l and closes a connection for the correspondingwire 46 associated with the carrier repeater No. 2. Inasmuch as thecontacts 23 and i9 have shifted upon the picking up of relay LTP thewires I for provided that the transfer in response to the actuation ofthe switch LTS at the control office is effective not only for theshifting from one pair of line wires to the other for both the lineportion extending between the control office and the repeater stationand the line portion extending between the repeater station and thefirst section of CTC territory, but it is also effective to transferfrom one carrier repeater unit to the other.

It Will be noted that the local direct curren power for operation of therespective carrier repeaters is selected by the relay CTR so as to applypower only to the particular carrier repeater that is used in thecarrier line circuit. Thus the closure of back contacts 4'! and 48 ofrelay CTR applies direct current power to the carrier re- 8 peater unit,No. 1, and front contacts 4'] and 48 applies directcurrentpower to thecarrier repeater unit No. 2.

If for some-reason it is desired to reverse the order of the associationof the respective carrier repeater units with the normal and standbyline wires so as to havethe carrier repeater No. 2

normally active when the line wires ILI lL2 ILI and lL 2 are in, use,the carrier repeater transfer switch CTS at the repeater station can beactuated to its right hand position to thus select thatthe relay CTR ispicked up in response to the closure of back contact 49 of relay LTP ascompared to the picking up of this relay through front contact 49 ofrelay LTP as has been described.

Assuming that the particular difficulty has been remedied in the linecircuits and/or carrier repeater unit that is normally used, transfercan be eifected back to these wires which have been described asbeingused under normal conditions.

In order to accomplishthis transfer back to the normal channels of linecircuit communication, the operator actuates the line transfer switchLTS back to its normally open position and thus allows the dropping awayof the relay LT. By the opening of front contacts l4 and I5, the wires2Ll and 2L2 are disconnected from the wires LI and L2 at the controloflice, and

the closure of back contacts l4 and I5 connects the wires [LI and IL2atvthe control office in a manner which has been described whenconsidering the normal conditions of the system. It is thus p rovidedthat direct current energy is applied from the battery CB to the wiresILI and iL2 at the control ofiice at a time when the relay LTP is pickedup at the repeater station, and thus a circuit is closed to energize-therelay LTI extending from the wire Ll at the control ofilce includingback contact M of relay LT, wire lLl front contact 22 of relay LTP,winding of relay LTI, front contact l8 of relay LTP, wire IL2 and backcontactl5 of relay LT, to wire L2. Upon the picking up of relay LTI, theopening of back contact 36 in the stick circuit for the relay LTP causesrelay LTP to be dropped away, and the dropping away of that relay opensthe connection through the repeater station that has been establishedthrough front contacts 33 and 34 of relay LTP, and closes circuitconnections to the wires lLl and IL2 through back contacts 22, I8, Hand23 to establish circuit connections which have been described whenconsidering the'normal conditions of the system.

Upon the dropping away of relay LTP, the circuit for relay LTI is openedat front contacts 22 and I8, and thus that relay is dropped away toclose back contact 36 and condition the stick circuit for the relay LTPso that it can be established upon subsequent transfer to the standbyline Wires.

Assuming the carrier repeater transfer switch C'IS to be in theleft-hand position as illustrated, the carrier transfer relay CTR'isdropped away upon the opening of its circuit at front contact 48 ofrelay LTP, and by the shifting of contacts 32, 21, 26 and 29 of relayCTR, the carrier repeater unit No. I is again rendered active and thecarrier repeater unit No. 2 inactive. The shifting of contacts l-l and48 of relay CTR disconnects the local source of power from the carrierrepeater unit No. 2 and connects such source to the carrier repeaterunit No. 1.

Having established continuityfrom the control oflice including wires, LIand L2, through the re- Meme 1 9 peaten stationt and-the normal-slime,wires 1L] and |L2, witn the relay; H119? it picked up the relaylLTl 1becomes energizedtthroughl front contents 20 and-.24 and r the t;picking 11p! ofthat relay by the'opening of backtcontact(M provides, forthe-.dropping away ofrtherelayLTPH Upon the dropping, away: oirelaytLTRl, the connections from wvires 2L! andu2L2. to. the, impedancematching,-trans.fiormer Zhthrough: frontfcontacts 38.-and 39, orrelay-LTB are opened, and the closures-of back; contacts :-20.:and 24sconnects ;the wires -IL.| and ALI? to the impedance matching transformerin a manner, which has, been .more

specifically described, whennconsidering the normal conditions ofthesystem.-. The opening of front contacts 24 andfld disconnects the:relay L 'lll andycauses that relay to be droppedtaway SGfBrStG closeback contact-M tosconditionthe stick oircuitior thet-relayl-LTP so thatsuch stick circuit can .be-established upon subsequent transfer: tOI,the standby wires- 2L1 and ZLZZ. This completes the restoration fromttheusesoft the standby lineawiresand standby carrier repeater unit No. 2 tothe normalline wireswand carrier repeater'unit No; lwWl'liCh areconsidered to be normally used-ltelecommunication purposes.

Although only a single repeater r station has been illustrated-in this iembodiment of the present invention; it *lSrtO, be understood that asmany repeater rstationslmay-be provided as are required in, practice;1the'stationrillustrated being typical of othen'stationsewhich canbezaddeds It is believed that, it should berreadily apparent that the:mode of: operation" where-a; plurality-of, repeater stations.isinvolvedsisr comparable to that which has been described: inwthatthestandby-line circuit is put-togetherinssteps fromlthe control office,and restoration to the line wireslnormally employedis accomplished in a:a similar a manner.

It is alsoto be understood1thatif the-linelcircuitwis shortenoughsotasnot-lto require-la: repeater stationrfor thercommunicationtof carrier current pulsesthatithe repeaterstat-ion canbe eliminated,land-under; SUChmCOIlditiOl'lS the respective rnormal Lands-standbypairs of; linenwires are unbroken between the controloificeaand, the beginningiof the CTC territory; Under such conditionsthe line. transfenmelays LTI and LTI will be energized directly from thecontrol office through the respective normal and standby pairs of i line:wireawitin which theyiare associated.

Although this embodiment aoftthe present invention is illustratedasbeingapplied to the use of a combination of direct currentand carriercurrent: communication line-z circuits, it is; to be understoodzthatthe.system'rof'line transfertthat 'isvhereinr discl osed ,is.equally rapplicable to; conditions Where only direct current or onlycarrier current communication line circuits are involved. If only directcurrent line circuits are involved, no repeater station is required, andthe normal and standby pairs of line wires are directly connected fromthe control offlce to the location at the beginning of CTC territory. Ifonly carrier current communication line circuits are involved, the linetransfer organization is provided as illustrated in the drawing exceptthat a source of direct current is necessarily connected to the wires Lland L2 at the control office as a means for energization of the linetransfer relays LTI and LT2. It is to be understood that such directcurrent energization would not necessarily have to be steady, but couldbe selected through a suitable transfer push-button or other momentarilyactuated means whereby the direct current would 10 be appliedito. the.line wires ,only, at times. when transferis to-be effected.

Hayingithus describedonespecific embodiment of. thepresentlinventionerelatinggto: means for transferring, a. linecircuitlofl'a centralized traffic control systemlirom one pair. of linewires to the other, it is desired to be, understood that this form isselected tolfacilitatethe disclosure iof the invention ratherthanntonlimitmthenum'ber of forms which thein entionmay-assume, and itis tobe further understood that various adaptations, alterations andmodifications. may-be applied totthe specific form: shown to meet therequirements of. practice .without in any manner departing-from. the.spirit, orscope of, thepresent invention: except as limited, by the.appending claims.

What. we claimtis:

1.1 In. aline circuit ;communication system for ,applying,communication,energy toa pair of controlwires atta locationlrcmote iroma controloffice, ,a normal and astandby pair. of line Wires extendingfrontthe-.oificevtorthe locatiomtmanur ally operable means at. the loiiicel for selectively applying energy; to. eitherfsaid. normallortsaid standby, pair of ulinecwires, normally deenergized transfer andsticktrelays-lat saidlocationnormally eiiective to connect.saidtnorrnalr pai'rtofline wires toisaid control wires; circuit .-meansfor connecting, said transfer. relay, acrossssaidrstandby pair of lineWires wherebyl saiditransfer relay is .picked upupon theapplication orenergy itoisaid standby pair of line Wiresattheofilceiby, saidinanuallyoperable means, circuitmeansforenergizingsaid stick-relayin response; tothe picking upi. of said transfer relay, aridmeansresponsive.tothe pickingup; of said stick ,relay f or disconnecting said transf en 1 rel ay,and. f or 1 transferringlth'e connection of said pair of control wiresfromvsaid normal l pair of line. wiresttobsaid lstandby, pair of linewires.

2, In: a ,line circuit communication system of thecharacter.ldescribedtfor applying energy to a pair.- of control1wires.attallocationmemotelfromia control office, aenorinaltand a.standby pairof line wireslextending fromitheloffice.toithe location,manually, operable means. at .1 theuoffice, forselectivelyapplyingenergy ,tdeithersaid. normal or said. standby. pair.ofeline. wires. a. normally .deenergizedv line transfer .relay atsaidilocation associated witheach, pair. of-.1ine.:wiries, ,a. nor,-mally deenergizedtransfer stick..relay atsaid location,circuit-means..forconnecting one, of said transfer relaysrtol sand-,stanby line wires .throughaaback contaot oflsaid stick relay,circuittmeans-forr connectinglthe other of said/transfer relays =tosaid: normalalinecw-ires :through. .a front contact of said stick relay,circuit means for energizing said stick relay in response to the pickingup of said one transfer relay and for deenergizing said stick relay inresponse to the picking up of said other transfer relay, and meansselected by said stick relay for selectively connecting said controlwires to said normal or said standby pair of wires.

3. In a line circuit communication system for maintaining communicationbetween a control office and a pair of communication wires at a remotelocation, the combination with normal and standby pairs of line wiresextending between the control oifice and the location and means forselectively applying direct current energy at the control ofiice to onepair of line wires or the other, of line transfer means at the .location comprising a normally deenergized line of said one transfer relay,and stick circuit means for said transfer stick relay effective tomaintain that relay picked up only so long as said other transfer relayis maintained dropped away.

4. In a line circuit communication system of the character described formaintaining communication between a control ofiice and a pair ofcommunication wires at a remote location, normal and standby pairs ofline wires extending between said office and said location, a repeaterstation between said control ofiice and said location at an intermediatepoint in said line wires, said repeater station having normal andstandby repeater units respectively associated with said normal andstandby pairs of line Wires, line transfer means including a stick relayat the repeater station selectively governed in accordance with theapplication of direct current to said normal or said standby pairs ofline wires at the control office, local energization means at therepeater station for each of said repeater units said means beingeffective to energize either said normal or said standby repeater unitas selected by said stick relay, and transfer means at said locationeffective in response to a shift in direct current energization at theoffice from one pair of line wires to the other to transfer theconnection of said pair of communication Wires at that location from oneof said pairs of line wires to the other.

5. In a line circuit communication system for communication by directcurrent and alternating current energy simultaneously over the same pairof line wires from a control ofii-ce to a pair of control wires at aremote location, a repeater station between said control office and saidlocation, said repeater station having normal and standby repeaterunits, normal and standby pairs of line wires extending between theoffice and the location through said repeater station, manually operablemeans at the control office for selectively energizing eithersaid'normal or said standby pair of line wires, a transfer stick relayat the repeater station effective to selectively connect said normal orsaid standby wires through said repeater station, said stick relay alsobeing effective to selectively connect said normal repeater unit or saidstandby repeater unit in the line circuit, electro-responsive means atthe repeater station normally connected through a back contact of saidstick relay to said standby wires, said electro-responsive means beingeffective to energize said stick relay in response to the energizationof said standby wires by said manually operable means, and means at saidlocation responsiVe to the energization of said standby wires fortransferring the connection of said pair of control wires at thatlocation from said normal pair of line wires to said standby pair ofline wires.

6. In a line circuit communication system for maintaining alternatingcurrent communication between a control ofiice and a pair ofcommunication wires at a remote location, normal and standby pairs ofline Wires extending between the control office and the location, arepeater station at an intermediate point in said line wires havingnormal and standby repeater units, manually operable means at thecontrol ofiice for selectively energizing either said normal or saidstandby pairs of line Wires with direct current, means at said repeaterstation for connecting said normal pair of line wires through saidnormal repeater unit for alternating current communication, normallydeenergized line transfer means at said repeater station responsive tothe energization of said standby wires at the control ofiice andeffective to connect said standby wires through said standby repeaterunit for alternating current communication, means at said repeaterstation for bypassing said repeater units for direct currentcommunication whereby the direct current applied to said normal or saidstandby pair of wires at the control office is applied eifectively tothe corresponding pair of line wires extending between said repeaterstation and said location, and normally deenergized line transfer meansat said location energized in response to the direct currentenergization of said standby line wires, said line transfer means beingefiective when deenergized to connect said normal line wires to saidpair of communication wires and effective when energized to connect saidstandby line wires to said pair of communication Wires.

FREDERICK W. BRIXNER. WILLIAM M. BARKER.

REFERENCES CITED The following referencesare of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,135,295 Stewart Nov. 1, 19382,171,751 Jackel Sept. 5, 1939

